Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $24.65   7.740%   $26.5579   $26.56   $26.55   $26.60  
  Purchase #2 $107.28   13.553%   $121.8197   $121.82   $121.80   $121.80  
  Purchase #3 $162.74   8.111%   $175.9398   $175.94   $175.95   $175.90  
  Purchase #4 $120.74   9.719%   $132.4747   $132.47   $132.45   $132.50  
  Purchase #5 $247.39   3.873%   $256.9714   $256.97   $256.95   $257.00  
  Purchase #6 $222.68   11.175%   $247.5645   $247.56   $247.55   $247.60  
  Purchase #7 $106.72   5.153%   $112.2193   $112.22   $112.20   $112.20  
  7 purchase totals = $992.20       $1,073.5473   $1,073.54   $1,073.45   $1,073.60